Counterbalancing tabletop construction

ABSTRACT

A counterbalancing mechanism for a table, such as a drafting table, having an angularly adjustable top. The mechanism is double acting, thereby counterbalancing the top against forward tipping forces when it is moved towards a horizontal position, and against rearward tipping forces when it is moved towards a vertical position, and is adjustable to control the onset and thereby the magnitude of such counterbalancing forces.

United States Patent Litvinoff et al.

[5 COUNTERBALANCING TABLETOP CONSTRUCTION [72] Inventors: James R. Litvinoif, Phillips; David F. Evans, Manitowoc, both of Wis.

[73] Assignee: American'llospital Supply Corporation, Evanston, Ill.

22 Filed: Jan.4, 1971 21] App]. N01: 103,528

[52] US. Cl ..108/2, 108/6 [51] Int. Cl. ..A47f 5/12 [58] Field of Search ..108/1-l0 [56] References Cited UNITED STATES PATENTS 2,356,924 8/1944 Froelich ..108l6 3,273,517 9/1966 Amthor, Jr. et al. ..108/2 [451 Oct. 17,1972

1,953,026 3/ 1934 Scheuer ..108l6 1,956,546 4/1934 Froelich 108/2 3,140,559 7/1964 Grow et al. ..108l6 3,364,881 1/1968 Koo] ..108/2 X Primary Examiner--Bobby R. Gay Assistant Examiner-Glenn O. Finch AttorneyDawson, Tilton, Fallon & Lungmus [5 7] ABSTRACT forces.

14 Claims, 6 Drawing Figures PATENTEDUBHY m2 3.698.327

SHEET 2 0F 2 FIG. 3

P'Hllli-J INVENTORA JAMES R. LITVINOFF DAVID F. EVANS ATT'YS COUNTERBALANCING TABLETOP CONSTRUCTION BACKGROUND holding the top in any selected angular position of ad justment may also be spaced a substantial distance from that line to exert more effectively the locking force for holding the top in any selected position of adjustment. Thus, in the aforementioned patent, the locking means takes the form of a coil spring mounted upon the adjustable top and adapted to grip an arcuate bar which is uniformly spaced from the tops pivot line. An operating lever is used to manipulate the coil spring for releasing its gripping force when re-positioning of the top into a different angle of adjustment is desired.

The pivot line for the top of a conventional drafting table, in addition to being spaced well below the top surface, is normally located closer to the rear edge of the top (i.e., the edge nearest a draftsman using the table) than to the tops forward edge. Consequently, when the top is in a generally horizontal position, its weight distribution tends to tip it forwardly, whereas when the top is in a steeply angled position, the distribution of weight behind the pivot line tends to tip the top rearwardly. While means for counterbalancing such tops have been known in the past, such mechanisms have been relatively complex and have lacked the adjustability necessary to vary the counterbalancing action in accordance with the preferences and needs of users. Stated differently, prior counterbalancing mechanisms, even if effective to counterbalance atop upon which nothing is supported, may be wholely inadequate when the unloaded balance is upset by the attachment to the top of relatively heavy drafting instruments, lamps, and other equipment desired by the user.

SUMMARY An important aspect of the invention therefore lies in providing a relatively simple and adjustable counterbalancing mechanism particularly suitable for use in conjunction with drafting tables and other tables having tiltable top surfaces. A specific object is to provide a counterbalancing mechanism which includes a single spring element capable of counterbalancing the top assembly against movement in either direction from a neutral position (or from a neutral range of positions) and, at the same time, a mechanism which is readily adjustable by the user so that the onset and thereby the magnitude of the counterbalancing force may be varied as desired.

The counterbalancing mechanism includes a spring in the form of a straight torsion bar which extends along the pivot axis of the top assembly or to the nonpivotal supporting frame assembly. Assuming that such end is secured to the top assembly, then the opposite end is operatively connected to the non-pivotal sup porting frame assembly; however, an adjustment mechanism is interposed between such frame assembly and the bar so that the onset of the counterbalancing action may be controlled in either direction of pivotal action of the top assembly. The result is that a user may readily adjust the mechanism so that the torsion spring will be in an untensioned state when the tabletop, along with the equipment which the user desires to attach to that top, is in a neutral or balanced state. Furthermore, such adjustability allows for a neutral range of selectively variable angular extent. The points of commencement of counterbalancing forces in opposite directions may therefore be varied independently of each other to suit the needs and preferences of the user. 7

Other objects and advantages. will appear from the specification and drawings.

DRAWINGS FIG. 1 is a side elevational view of a drafting table equipped with the counterbalancing mechanism of the invention, the unit being shown with the top assembly in a generally horizontal position;

FIG. 2 is a view similar to FIG. 1 but showing the top assembly in a steeply inclined position;

FIG. 3 is an exploded perspective view illustrating the major components of the counterbalancing mechanism of the invention;

FIG. 4 is a broken rear elevational view with non-essential parts omitted to illustrate more clearly the relationship between the counterbalancing mechanism and other elements of the table;

FIG. 5 is a somewhat schematic view illustrating the relationship of the stop plate and the adjustable elements when the tabletop is in the horizontal position of FIG. 1;

FIG. 6 is a view similar to FIG. 5 but showing the relationship of parts when the table surface is in the inclined position of FIG. 2.

DESCRIPTION Referring to the drawings, numeral 10 generally designates a drafting table as illustrative of a type of table for which the counterbalancing mechanism of the invention is particularly suited. The table includes a base 11 which supports a frame assembly 12 having a pair of upstanding frame members or standards 12a. A parallelogram linkage 13 connects the base 11 and frame 12 to permit vertical adjustability of the frame, all as well known in the art (see U.S. Pat. No. 2,356,924). Since the linkage arrangement, its operation, and its connecting elements are all known in the art and constitute no part of the present invention, further discussion of those elements is believed unnecessary herein.

A tabletop assembly 14 is pivotally supported by the upstanding members of frame assembly 12 for movement between a' generally horizontal position (FIG. 1) and a generally vertical position. The particular angle selected depends upon the preference of the user. Further, the preference of one draftsman may change depending upon the particular project involved, the area of the board on which the drafting work is taking place, and the desire of the user to perform work in a standing or a seated position.

The top assembly 14 includes a tabletop l5 and a pair of depending arms 16 which. are pivotally connected at their lower ends to the upstanding frame member 12 by a pair of pins 17 or by any other suitable pivot elements. It will be observed that the pivot line passing through pins 17 is parallel with the surface of topbut is spaced a substantial distance beneath the tabletop. It will also be observed that the pivot line is spaced more closely to the front or leading edge 15a of the tabletop than to the rear edge 15b thereof. The result is that, in the absence of some counterbalancing means, a tabletop in the position shown in FIG. 1 would tend to tip forwardly in a counterclockwise direction whereas a table top in the position shown in FIG. 2 would tend to tip rearwardly in a clockwise direction.

A suitable locking mechanism 18 is provided for locking the tiltable tabletop in any selected position of adjustment. In the particular illustration given, such mechanism comprises a pair of arcuate bars 19 secured to each of the upstanding frame members 12a. Each of the bars extends along a plane normal to the pivot axis of the top and is spaced a substantial but uniform distance from that axis. Locking elements in the form of coil torsion springs 20 normally grip the bars 19 with sufficient force to prevent relative movement between the parts. The springs are carried at the opposite ends of a horizontal operating member 21 rotatably mounted upon arms 16 and a handle 22 projects rearwardly from the rotatable operating member to permit manual rotation of the springs 20 into positions wherein the gripping forces exerted upon arcuate members 19 are relieved. If desired, spring means (not shown) may be provided to rotate member 21 to provide increased locking force between coil springs 20 and arcuate bars 17. The locking mechanism thus described is essentially the same as disclosed in U.S. Pat. No. 2,356,924 and, since such a construction is well known in the art, further description is believed unnecessary for purposes of the present disclosure.

The counterbalancing mechanism for the top assembly is illustrated most clearly in FIGS. 3 and 4 and is designated generally by the numeral 23. Such mechanism includes a torsion bar 24 which extends along the horizontal pivot line of the top assembly between upstanding frame members 12a. One end 24a of the torsion bar is rigidly secured by means of attachment member 25 to arm 16 of the top assembly. The opposite end 24b of the torsion bar is operatively secured by means hereinafter described to the nonpivotal frame assembly 12. Consequently a twisting action of the torsion bar occurs as the top assembly is pivoted from one extreme to the other, the resistance to such twisting produced by the spring material of the bar giving rise to the desired counterbalancing action in both directions. Although end 24b of the bar has been described as being operatively connected to the frame assembly 12, an adjustment mechanism is in fact interposed between the parts to provide a limited range of lost motion in a neutral zone and to permit selective and independent adjustment of the points at which counterbalancing force commences as the top assembly is moved in either direction from its neutral position.

The adjustment mechanism comprises a pair of adjustment elements in the form of vertical pivot plates 26 and 27 secured to end portion 24b of the torsion bar. To facilitate such attachment and to insure against relative rotation of the plates with respect to the bar, the bar is preferably formed with a non-circular cross sectional configuration. The plates are apertured to he slid in place upon end portion 24b of the bar and may be welded or otherwise fixed in position. A bushing 28 is disposed between the plates and serves as a spacer during assembly of the parts.

A stop plate 29 is disposed between pivot plates 26 and 27, the stop plate being provided with an opening 29a which rotatably receives bushing 28. The vertical stop plate 29 is fixed to one of the upstanding frame members 12a and, as shown most clearly in FIG. 3, is provided with an arcuate recess 30 which defines a curved or arcuate edge disposed at a substantially uniform distance from the pivot axis. The arcuate recess terminates in a pair of circumferentially spaced stop shoulders 31 and 32.

It will be observed from FIG. 3 that pivot plates 26 and 27 are each provided with a pair of arcuate slots 26a-26 and 27a-27b, respectively. The slots of the respective pivotplates register with each other and with recess 30, and interconnecting stop members in the form of bolts 33 and 34 extend through the slots and recess. Spacer sleeves 35 and 36 extend about the portions of the bolts between pivot plates 26 and 27, such spacer sleeves having axial dimensions slightly greater than the width of stop plate 29. Consequently, even when bolts 33 and 34 are fully tightened, the spacing between pivot plates 26 and 27 will be slightly greater than the thickness of the stop plate 29.

Since the slots 26a, 26b, 27a and 27b are arcuate and elongated, it is believed apparent that by selective positioning of bolts 33 and 34 a limited range of pivotal movement of the top assembly, free of application of any spring counterbalancing force, may be provided. The maximum range of free or lost motion is achieved by shifting the bolts together as closely as possible. Conversely, the free travel may be substantially if not completely eliminated by positioning the bolts as far away from each other as possible. A particularly important aspect of the invention lies in the fact that the onset of counterbalancing force in either direction of movement may be precisely controlled by locating each of the respective bolts 33 and 34 independently of the other.

Thus, referring to FIG. 5, it will be observed that forward pivotal movement of the top assembly in the direction represented by arrow 37 will be resisted or counterbalanced by torsion spring 24 because the shaft of stop member or bolt 33 engages the shoulder 32 of stop plate 29. However, if the user of the table had desired to delay the onset of the counterbalancing force when the top assembly is shifted forwardly, he would have re-positioned bolt 33 at a lower position along slot 26a.

Similarly, commencement of the counterbalancing force as the top assembly is shifted towards a vertical position may be adjusted by varying the position of bolt 34 in slots 26b and 27b. With the top assembly in the inclined position shown in FIG. 6, the weight of that assembly exerts a downward force in the direction of arrow 38 and such force is resisted or counterbalanced by torsion bar 24 upon which a twisting action has occurred following engagement between bolt 34 and stop shoulder 31. The position of bolt 34 in slot 26b (FIG. 6) reveals that the onset of the counterbalancing force (as the top is moved in the direction of arrow 38) has been and preferences of the user. Those needs are in turn dependent to a large extent upon the equipment which the user elects to place upon the top assembly. A heavy lamp may require one position of adjustment and the addition of other equipment, such as a drafting instrument, may require another.

It is particularly significant that by means of the adjustment mechanism, a range of movement of the top assembly may be provided which is neutral or free of counterbalancing force despite the fact that a torsion bar is utilized which does not of itself provide for a such a range of movement.

In the construction described above, a pair of pivotal plates 26 and 27 have been disclosed; however, it is believed apparent that similar results might be achieved if only a single pivot plate or adjustment element were used. Thus, the adjustment mechanism might include pivot plate 26 as one adjustment element and stop plate 29 as the other. However, the addition of the second pivot plate 27 adds greater strength to the unit and greatly simplifies the adjustable mounting of stop members or bolts 33 and 34.

While in the foregoing we have disclosed an embodiment of the invention in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.

We claim 1. A table having a top assembly mounted upon a frame assembly for pivotal movement about a horizontal pivot line extending between a pair of upstanding frame members of said frame assembly, wherein the improvement comprises a counterbalancing mechanism including a generally horizontal torsion bar extending along said pivot line between said frame members, said bar being secured at one end to one of the two assemblies and having its opposite end secured to an adjustment element, a second adjustment element being in juxtaposition relative to said first-mentioned adjustment element and being fixed to the other of the two assemblies, and means operatively interconnecting said first and second adjustment elements and limiting the extend of pivotal movement of said first adjustment element relative to said second adjustment element as said top assembly is pivoted in either direction about said axis.

2. The structure of claim 1 in which said first adjustment element comprises at least one vertical pivot plate secured to said opposite end of said bar, said second adjustment element comprising a stop plate secured to said other of said assemblies and parallel with said pivot plate.

3. The structure of claim 2 in which said stop plate is provided with a recess terminating at its ends in a pair of circumferentially spaced stop shoulders, said means comprising at least one stop member secured to said pivot plate and projecting horizontally therefrom into said recess for engagement with said stop shoulders as said top assemblyis pivoted in opposite directions.

4. The structure of claim 3 in which said stop member is movably secured to said pivot plate for adjustment in a circumferential direction into any of a variety of selected positions.

5. The structure of claim 3 in which a pair of said stop members are provided, said members being spaced apart within said recess.

6. A table having a top assembly mounted upon a frame assembly for pivotal movement about a horizontal pivot line extending between a pair of upstanding frame members of said frame assembly, wherein the improvement comprises a counterbalancing mechanism including a generally horizontal torsion bar extending along said pivot line between said members, said bar being secured at one end to a pair of spaced vertical pivot plates, a vertical stop plate disposed between said pivot plates and provided with a recess terminating in a pair of circumferentially spaced stop shoulders, and at least one stop member extending between said pivot plates and secured thereto, said stop member extending through said recess for engagement with at least one of said shoulders.

7. The structure of claim 6 in which said stop member is movably secured to said pivot plates for adjustment in a circumferential direction into any of a variety of positions relative thereto.

8. The structure of claim 7 in which said stop member comprises a bolt extending through aligned arcuate slots in said pivot plates, said bolt being securable in any of a variety of positions along the length of said slots.

9. The structure of claim 6 in which a pair of said stop members are provided, said members being spaced apart within said recess.

10. The structure of claim 9 in which said stop members are movably secured to said pivot plates for adjustment towards and away from each other into any of a variety of selected relative positions.

11. The structure of claim 10 in which each of said pivot plates is provided with a pair of spaced circumferentially elongated slots, the slots of the respective plates being in paired alignment,.said stop members comprising a pair of bolts extending through said slots and securable in any of a variety of relative positions therein for abutment with the stop shoulders of said stop plate.

12. A table having a top assembly mounted upon a frame assembly for pivotal movement about a horizontal pivot line extending between a pair of upstanding frame members of said frame assembly, wherein the improvement comprises a counterbalancing mechanism including a generally horizontal torsion bar extending along said pivot line between said frame members, said bar being secured at one end to one of the two assemblies and having its opposite end secured to an adjustment element, a second adjustment element being in juxtaposition relative to said first-mentioned adjustment element and being fixed to the other of the two assemblies, and means operatively interconnecting said first and second adjustment elements and limiting the extent of pivotal movement of said first adjustment element relative to said second adjustment element as said top assembly is pivoted about said axis, said first adjustment element comprising at least one vertical pivotal plate secured to said opposite end of said bar and said second adjustment element comprising a stop plate secured to said other of said assemblies and parallel with said pivot plate, said stop plate being provided with a recess terminating at its ends in a pair of circumferentially spaced stop shoulders, said means comprising at least one bolt secured to said pivot plate and projecting horizontally therefrom into said recess for engagement with said stop shoulders as said top assembly is pivoted in opposite directions, said bolt extending through an arcuate slot in said pivot plate and being movably secured to said pivot plate for circumferential adjustment into any of a variety of selected positions along the length of said slot.

13. A table having a top assembly mounted upon a frame assembly for pivotal movement about a horizontal pivot line extending between a pair of upstanding frame members of said frame assembly, wherein the improvement comprises a counterbalancing mechanism including a generally horizontal torsion bar extending along said pivot line between said frame members, said bar being secured at one end to one of the two assemblies and having its opposite end secured to an adjustment element, a second adjustment element being in juxtaposition relative to said first-mentioned adjustment element and being fixed to the other of the two assemblies, and means operatively interconnecting said first and second adjustment elements and limiting the extent of pivotal movement of said first adjustment element relative to said second adjustment element as said top assembly is pivoted about said axis, said stop plate being provided with a recess terminating at its ends in a pair of circumferentially spaced stop shoulders, said means comprising a pair of stop members secured to said pivot plate and projecting horizontally therefrom into said recess for engagement with said stop shoulders as said top assembly is pivoted in opposite directions, said stop members being spaced apart within said recess and being movably secured to said pivot plate for adjustment in circumferential directions into any of a variety of selected positions.

14. The structure of claim 13 in which said pivot plate is provided with a pair of circumferentially spaced arcuate slots, each of said stop members comprising a bolt extending through one of said slots and being securable in any of a variety of positions along the length thereof. 

1. A table having a top assemblY mounted upon a frame assembly for pivotal movement about a horizontal pivot line extending between a pair of upstanding frame members of said frame assembly, wherein the improvement comprises a counterbalancing mechanism including a generally horizontal torsion bar extending along said pivot line between said frame members, said bar being secured at one end to one of the two assemblies and having its opposite end secured to an adjustment element, a second adjustment element being in juxtaposition relative to said firstmentioned adjustment element and being fixed to the other of the two assemblies, and means operatively interconnecting said first and second adjustment elements and limiting the extent of pivotal movement of said first adjustment element relative to said second adjustment element as said top assembly is pivoted in either direction about said axis.
 2. The structure of claim 1 in which said first adjustment element comprises at least one vertical pivot plate secured to said opposite end of said bar, said second adjustment element comprising a stop plate secured to said other of said assemblies and parallel with said pivot plate.
 3. The structure of claim 2 in which said stop plate is provided with a recess terminating at its ends in a pair of circumferentially spaced stop shoulders, said means comprising at least one stop member secured to said pivot plate and projecting horizontally therefrom into said recess for engagement with said stop shoulders as said top assembly is pivoted in opposite directions.
 4. The structure of claim 3 in which said stop member is movably secured to said pivot plate for adjustment in a circumferential direction into any of a variety of selected positions.
 5. The structure of claim 3 in which a pair of said stop members are provided, said members being spaced apart within said recess.
 6. A table having a top assembly mounted upon a frame assembly for pivotal movement about a horizontal pivot line extending between a pair of upstanding frame members of said frame assembly, wherein the improvement comprises a counterbalancing mechanism including a generally horizontal torsion bar extending along said pivot line between said members, said bar being secured at one end to a pair of spaced vertical pivot plates, a vertical stop plate disposed between said pivot plates and provided with a recess terminating in a pair of circumferentially spaced stop shoulders, and at least one stop member extending between said pivot plates and secured thereto, said stop member extending through said recess for engagement with at least one of said shoulders.
 7. The structure of claim 6 in which said stop member is movably secured to said pivot plates for adjustment in a circumferential direction into any of a variety of positions relative thereto.
 8. The structure of claim 7 in which said stop member comprises a bolt extending through aligned arcuate slots in said pivot plates, said bolt being securable in any of a variety of positions along the length of said slots.
 9. The structure of claim 6 in which a pair of said stop members are provided, said members being spaced apart within said recess.
 10. The structure of claim 9 in which said stop members are movably secured to said pivot plates for adjustment towards and away from each other into any of a variety of selected relative positions.
 11. The structure of claim 10 in which each of said pivot plates is provided with a pair of spaced circumferentially elongated slots, the slots of the respective plates being in paired alignment, said stop members comprising a pair of bolts extending through said slots and securable in any of a variety of relative positions therein for abutment with the stop shoulders of said stop plate.
 12. A table having a top assembly mounted upon a frame assembly for pivotal movement about a horizontal pivot line extending between a pair of upstanding frame members of said frame assembly, wherein the improvement comprises a counterbalancing mEchanism including a generally horizontal torsion bar extending along said pivot line between said frame members, said bar being secured at one end to one of the two assemblies and having its opposite end secured to an adjustment element, a second adjustment element being in juxtaposition relative to said first-mentioned adjustment element and being fixed to the other of the two assemblies, and means operatively interconnecting said first and second adjustment elements and limiting the extent of pivotal movement of said first adjustment element relative to said second adjustment element as said top assembly is pivoted about said axis, said first adjustment element comprising at least one vertical pivotal plate secured to said opposite end of said bar and said second adjustment element comprising a stop plate secured to said other of said assemblies and parallel with said pivot plate, said stop plate being provided with a recess terminating at its ends in a pair of circumferentially spaced stop shoulders, said means comprising at least one bolt secured to said pivot plate and projecting horizontally therefrom into said recess for engagement with said stop shoulders as said top assembly is pivoted in opposite directions, said bolt extending through an arcuate slot in said pivot plate and being movably secured to said pivot plate for circumferential adjustment into any of a variety of selected positions along the length of said slot.
 13. A table having a top assembly mounted upon a frame assembly for pivotal movement about a horizontal pivot line extending between a pair of upstanding frame members of said frame assembly, wherein the improvement comprises a counterbalancing mechanism including a generally horizontal torsion bar extending along said pivot line between said frame members, said bar being secured at one end to one of the two assemblies and having its opposite end secured to an adjustment element, a second adjustment element being in juxtaposition relative to said first-mentioned adjustment element and being fixed to the other of the two assemblies, and means operatively interconnecting said first and second adjustment elements and limiting the extent of pivotal movement of said first adjustment element relative to said second adjustment element as said top assembly is pivoted about said axis, said stop plate being provided with a recess terminating at its ends in a pair of circumferentially spaced stop shoulders, said means comprising a pair of stop members secured to said pivot plate and projecting horizontally therefrom into said recess for engagement with said stop shoulders as said top assembly is pivoted in opposite directions, said stop members being spaced apart within said recess and being movably secured to said pivot plate for adjustment in circumferential directions into any of a variety of selected positions.
 14. The structure of claim 13 in which said pivot plate is provided with a pair of circumferentially spaced arcuate slots, each of said stop members comprising a bolt extending through one of said slots and being securable in any of a variety of positions along the length thereof. 